That's my point exactly. They sell them to other people to ensure that doesn't happen. Now I'm not actually sure if they produce enough for that to be relevant

That's my point exactly. They sell them to other people to ensure that doesn't happen. Now I'm not actually sure if they produce enough for that to be relevant. But my understanding is they dominate the asic market and asics are the only thing that are profitable for mining bitcoin. It could be if they didn't sell and mined themselves they would have enough mining share to cause people to lose faith in the currency and crash the market.